JP2012246159A - Sealing structure of drawing furnace for optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sealing structure of a drawing furnace for optical fiber which enables sealing clearances produced between the upper-end opening of the drawing furnace for optical fiber and an optical fiber preform by means of a simple and damage-resistant structure even when the optical fiber varies high in diameter.SOLUTION: The sealing structure is such that a seal member 30 composed of a discontinuous ring in which a part 31 of the ring is cut, and containing carbon as a main ingredient is so installed that the inner surface of the seal member 30 is brought into contact with the side surface of the optical fiber preform by a contraction force in the radial direction of the seal member 30 in the state that the optical fiber is passed on the inner periphery side of the seal member 30.

Description

  The present invention relates to a sealing structure for an optical fiber drawing furnace for sealing a gap between an upper end opening of an optical fiber drawing furnace and an optical fiber preform.

  For example, the optical fiber is drawn by heating an optical fiber preform formed of quartz as a main component in a drawing furnace. Carbon is mainly used as the in-furnace part material of this drawing furnace, and in order to prevent oxidation of this carbon, rare gas such as helium and argon or nitrogen gas (hereinafter referred to as inert gas) is used in the furnace. It is filled inside.

Further, by making the pressure inside the furnace positive, air outside the furnace (oxygen) is prevented from entering the furnace, but the gap of the inlet of the optical fiber preform at the upper end of the drawing furnace, In other words, if the air gap is not well removed (not sealed) in the gap between the upper end opening of the drawing furnace and the optical fiber preform, air outside the furnace will be entrained.
Therefore, a sealing mechanism that seals the gap at the upper end of the drawing furnace is necessary so that outside air is not caught in the furnace. If this portion can be well sealed, the amount of inert gas used can be reduced, which can lead to cost reduction.

  Patent Document 1 discloses an optical fiber drawing device having a seal structure. This drawing device is located directly above the XY table, an XY table provided with an insertion port through which the optical fiber preform passes, an inner diameter variable seal mechanism disposed on the inner periphery of the insertion port, and the XY table. An outer diameter measuring means for measuring the outer diameter of the optical fiber preform, and a deviation amount measuring means for measuring the deviation amount of the optical fiber preform with respect to the X-direction center of the XY table and the deviation amount with respect to the Y-direction center. ing. Here, a CCD camera is provided as the outer diameter measuring means and the deviation amount measuring means.

  Further, this drawing apparatus controls the movement of the XY table so that the center position of the XY table coincides with the center of the optical fiber preform based on the measurement data of the deviation amount measuring means, and the outer diameter. Based on the measurement data of the measuring means, there is provided control means for performing contraction control so that the inner diameter of the seal mechanism is always maintained at a constant clearance with respect to the outer diameter of the optical fiber preform.

  Patent Document 2 discloses an upper seal ring installed at the upper end of the drawing furnace body so as to surround the optical fiber preform, and a telescopic mechanism for applying a force to the outer periphery of the upper seal ring in the center direction of the upper seal ring. And a seal structure that seals the gap at the upper end of the draw furnace body so that the upper seal ring is always in close contact with the optical fiber preform. Here, the upper seal ring includes an inner seal ring configured by connecting a plurality of inner seal ring pieces, and an outer seal ring configured by connecting a plurality of outer seal ring pieces disposed on the outer periphery thereof. Further, the connecting portion of the inner seal ring piece and the connecting portion of the outer seal ring piece are arranged so as not to overlap each other.

  Patent Document 3 discloses a technique of providing a ring-shaped seal member around an optical fiber preform as a seal structure in an optical fiber drawing furnace. 4A and 4B are diagrams showing this seal structure, in which FIG. 4A is a cross-sectional view of the seal structure, FIG. 4B is a top view of a carbon sheet without slits, and FIG. 4C is a top view of a carbon sheet with slits. FIG.

  As shown in FIG. 4A, the seal structure 50 is provided on the upper end surface (and the upper end surface of the core tube 12) of the furnace casing 11 of the optical fiber drawing furnace. In the seal structure 50, a purge gas introduction pipe 58 is provided in a cylinder 57 with an upper lid serving as an outer wall of the seal structure 50, and seal members 51, 52, and 53 are provided in multiple layers around the optical fiber preform 1. The seal members 52 and 53 are placed on the sheet support member 59. Among them, the seal member 51 is formed so that the non-slit carbon sheet 61 of FIG. 4 (B) is placed on the upper end surface of the furnace casing 11 and is cut from the inner periphery as shown in FIG. 4 (C). The carbon sheet 63 provided with the inner peripheral slit 63a and the outer slit 63b formed so as to cut from the outer periphery is placed, and the non-slit carbon sheet 62 of FIG. 4B is placed thereon. Is formed. Finally, the upper part is pressed by the sheet presser 64.

Japanese Patent Laid-Open No. 10-167751 JP 2006-342030 A JP 2010-173895 A

Regarding the sealing structure of the upper end opening of the drawing furnace described above, if the variation of the optical fiber preform diameter is small, the gap between the upper end opening of the drawing furnace body and the optical fiber preform is simply set according to the preform diameter. If it is closed, a sufficient sealing effect can be obtained.
However, when the variation of the optical fiber preform diameter is as large as about ± 5 mm or more, for example, the gap interval fluctuates greatly. Therefore, a seal structure that can be sealed while taking into account the variation of the gap is required. .

However, in the seal structure described in Patent Document 1, a shutter plate is provided as a variable-diameter seal mechanism that can uniformly deform the inner diameter. Based on the measurement result of the CCD camera, the shutter plate It is necessary to perform electronic control such as reducing the opening diameter, and the mechanism is complicated and expensive.
Further, since the seal structure described in Patent Document 2 is a structure in which the seal ring pieces are connected, when the diameter variation of the optical fiber preform is large in the longitudinal direction, it is difficult to follow the diameter variation.

  The sealing structure described in Patent Document 3 is a structure in which a carbon sheet with slits is provided around an optical fiber preform to seal a gap generated in the upper end opening, but the stretchability of the carbon sheet is limited. Therefore, the diameter variation in the longitudinal direction of the optical fiber preform is only about ± 2 mm.

  The present invention has been made in view of the above circumstances, and its purpose is to provide an upper end opening and an optical fiber preform in an optical fiber drawing furnace even if the optical fiber preform has a large diameter variation. It is an object of the present invention to provide a sealing structure for an optical fiber drawing furnace that makes it possible to seal a gap generated between the optical fiber and the optical fiber with a structure that is simple and hardly damaged.

  The optical fiber drawing furnace sealing structure according to the present invention is a structure for sealing a gap between the upper end opening of the optical fiber drawing furnace and the optical fiber preform inserted from the upper end opening. is there. And this seal structure consists of a discontinuous ring in which a part of the ring is cut, and a seal member mainly composed of carbon is passed through an optical fiber preform on the inner peripheral side of the seal member. The seal member is provided so that the inner surface of the seal member is in contact with the side surface of the optical fiber preform by the contracting force in the radial direction of the seal member.

The seal structure preferably includes a sleeve so as to cover a cut portion of the seal member.
Further, the seal member is preferably composed of a plurality of cut rings, and is overlapped so as to shift the cut portions of the rings, and the cross section is preferably a quadrangle. Furthermore, it is preferable that the ratio of the thickness of the cross section and the width in the radial direction of the sealing member is thickness / width ≧ 0.2.
The sealing member preferably has a heat resistance of 200 ° C. or higher.
Moreover, it is preferable that a ring-shaped member having heat resistance and not discontinuity is further provided on the upper and / or lower part of the sealing member.

  According to the present invention, even with an optical fiber preform having a large diameter variation, a gap generated between the upper end opening in the optical fiber drawing furnace and the optical fiber preform is sealed with a simple and hardly damaged structure. It becomes possible.

It is a figure for demonstrating the outline of the seal structure and optical fiber wire drawing furnace body which concern on this invention. It is a figure which shows an example of the seal structure which concerns on this invention, and is sectional drawing which shows the detail of the seal structure in FIG. It is a figure which shows the principal part of the seal structure of FIG. It is sectional drawing which shows the seal structure by a prior art.

FIG. 1 shows an example of a sealing structure according to the present invention and an optical fiber drawing furnace body, in which 1 is an optical fiber preform (glass preform for optical fiber) and 10 is a main body of the optical fiber draw furnace. (Hereinafter simply referred to as a drawing furnace body), 20 is a seal structure, and 40 is a lid.
As shown in FIG. 1, a draw furnace body 10 includes a furnace casing 11, a core tube 12 provided therein, a cylindrical heating source (heater) 13 provided on the outer periphery of the core tube 12, And a heat insulating material 14 provided on the outer periphery of the heater 13.

  The core tube 12 accommodates the optical fiber preform 1 inserted from the upper end opening. The heater 13 heats and melts the optical fiber preform 1 accommodated in the core tube 12. Further, the drawing furnace body 10 is provided with an inert gas supply mechanism (not shown) so as to supply inert gas or the like in the furnace core tube 12 or around the heater 13 to prevent oxidation or deterioration. It has become.

In the drawing furnace body 10, the optical fiber preform 1 can be moved in the drawing direction (downward direction) by a separately provided moving mechanism. The support rod 2 for suspending and supporting the optical fiber preform 1 from above is connected.
The support rod 2 may be formed integrally with the optical fiber preform 1 or may be separately manufactured and fused. Although the circular shape is mentioned as a cross-sectional shape of the support rod 2, it is not restricted to it. Further, in order to connect the support rod 2 and the optical fiber preform 1, a connection part (fitting part) may be provided separately.

  In addition, although the upper end part of the inner wall of the core tube 12 forms the upper end opening part in the upper end part 11a of the drawing furnace body 10 as it is in FIG. 1, the example is not restricted to this. For example, an upper lid that is a narrower upper end opening than the inner diameter d of the core tube 12 may be provided on the upper side of the core tube 12, and in this case, the gap to be sealed is the narrow upper end opening and the optical fiber preform 1. It becomes a gap generated between the two. In addition, the cross-sectional shape of the optical fiber preform 1 is basically generated with the aim of a perfect circle, but there may be some unevenness regardless of the accuracy, and it may be elliptical. May be. The upper end opening may have a circular cross section, but this accuracy does not matter.

  An optical fiber drawing process in the drawing furnace body 10 described above will be schematically described. In the drawing furnace body 10, the lower part of the optical fiber preform 1 in the furnace is heated by the heater 13 in the furnace core tube 12 while preventing outside air from being entrained by a seal structure 20 described later provided at the upper end portion 11 a. . In the draw furnace body 10, the optical fiber 3 is melted and drooped from the lower end of the optical fiber preform 1 which has been heated and melted to have a small diameter, and the discharge hole 16 provided in the lower end portion of the furnace casing 11 The optical fiber 3 is pulled out. Then, as the drawing progresses, the optical fiber preform 1 is gradually lowered together with the support rod 2 by the moving mechanism.

  The seal structure 20 according to the present invention includes a through hole (that is, an upper end opening) provided for penetrating (slowly inserting) the optical fiber preform 1 having a circular cross section at the upper end portion 11a of the drawing furnace body 10. It is a structure for sealing the clearance gap 15 produced between the optical fiber base materials 1 of the circular cross section inserted from 1st.

  Hereinafter, the main features of the seal structure 20 according to the present invention will be described with reference to FIGS. Here, FIG. 2 is a cross-sectional view showing details of the seal structure 20. 3 is a diagram showing the main part of the seal structure of FIG. 2, FIG. 3 (A) is a perspective view thereof, FIG. 3 (B) is a top view thereof, FIG. 3 (C) is another example of FIG. FIG. The lid 40 will be described later.

  The seal structure 20 illustrated in FIG. 2 includes a housing (housing portion) 27 that is a hollow disk-shaped member, and includes a seal member 30 described later therein. The housing 27 is provided with a gas inlet 27a through which an inert gas or the like is supplied by a supply mechanism (not shown). Among the internal members, at least the seal member 30 uses carbon as will be described later, and an inert gas or the like spreads from the gas inlet 27a to the inside of the housing 27, so that the members such as the seal member 30 are oxidized. Deterioration can be prevented. In addition, the inert gas etc. here may be the same as the gas supplied into the furnace, or may be different types.

  A sleeve portion 21 is provided on the upper side of the housing 27. This sleeve portion 21 is designed so that the inner diameter matches the maximum diameter of the optical fiber preform 1 and prevents the entry of outside air by forming a narrow gap at the top. The sleeve portion 21 is preferably long in order to prevent intrusion of outside air. On the other hand, the sleeve portion 21 needs to be high enough not to interfere with other parts during the drawing process. Further, the closer the inner diameter of the sleeve portion 21 is to the maximum diameter of the optical fiber preform 1, the narrower the gap can be. However, it is necessary to have a gap that does not collide with the optical fiber preform 1 due to “bending” or the like. . By providing the sleeve portion 21 having such a shape, the gas in the furnace can be made more difficult to leak.

  In the example of FIG. 2, the carbon sheet 26, the quartz ring 25, the carbon sheet 26, the carbon sheet 24 with notches, the carbon sheet 26, the carbon sheet 24 with notches, the seal member 30, and the carbon sheet are sequentially arranged from the bottom of the housing 27. 26, a carbon sheet 24 with cuts, and a carbon sheet 26 are laminated. In addition, since airtightness is ensured by the sealing member 30 which is the main feature of the present invention, members such as the carbon sheet 26 and the carbon sheet 24 with notches provided for the purpose of assisting the sealing performance are not necessarily required. By combining with these members, sealing properties can be further secured. These members such as carbon sheets may be stacked in several layers, and several sets of members stacked in several layers may be provided.

  And in this invention, the sealing member 30 which consists of a discontinuous ring which cut | disconnected the part 31 of the ring and which has carbon as a main component is used. More specifically, in the seal structure 20 according to the present invention, the optical fiber preform is caused by the contraction force in the radial direction of the seal member 30 in a state where the optical fiber preform 1 is passed through the inner peripheral side of the seal member 30. The inner surface of the seal member 30 is provided in contact with the side surface of the material 1.

  As a material used for the seal member 30, a material mainly composed of carbon is used. This is because carbon not only has excellent heat resistance but also can be processed with a small coefficient of friction (a soft material), so there is no fear of damaging the optical fiber preform 1 even if it comes into contact. Carbon is also preferred because it can be easily molded by press molding or the like. As carbon, it is preferable to use what is called high purity carbon from a viewpoint of impurity mixing.

  The above-described cutting portion 31 is a cut portion that is inserted in one place in the circumferential direction, and the inner diameter of the seal member 30 is flexibly changed by changing the opening degree of the gap. The cut portion 31 may be cut obliquely as illustrated in FIG. 3A, or may be cut straight (that is, along a cross section perpendicular to the circumferential direction of the seal member 30). Good. When the optical fiber preform 1 is inserted inside the seal member 30, the opening degree of the gap changes following the outer diameter of the optical fiber preform 1, so that even if the outer diameter of the optical fiber preform 1 changes. The seal member 30 continues to contact the optical fiber preform 1. At this time, the force that the seal member 30 presses against the optical fiber preform 1 is weak enough not to inhibit the lowering of the optical fiber preform 1.

As a result, as illustrated in FIG. 2, the optical fiber preform 1 is lowered as indicated by an arrow as the drawing progresses, and the outer diameter of the optical fiber preform 1 is, for example, from φ ₁ to φ ₂ (> φ ₁ ). Even if the seal member 30 increases, the seal member 30 can extend outward or shrink on the contrary, and can automatically absorb the diameter variation of the optical fiber preform 1.

  As described above, in the seal structure 20 according to the present invention, the seal member 30 contracts in the radial direction to follow the change in the outer diameter of the optical fiber preform 1, and as a result, in the longitudinal direction of the optical fiber preform 1 It can cope with diameter fluctuation. Specifically, by utilizing the flexibility of carbon as a main component, even if the outer diameter fluctuation is about ± 5 to 15 mm (about 10% of the optical fiber preform diameter), the surface circumference of the optical fiber preform 1 is increased. It is possible to ensure close airtightness.

  In addition, as shown in FIG. 2, the sealing member 30 preferably has a quadrangular cross section (that is, a cross section perpendicular to the circumferential direction) in terms of ensuring airtightness. Further, the portion other than the cut portion 31 of the seal member 30 is formed by the thickness D and the radial width R shown in FIGS. The ratio D / R is preferably D / R ≧ 0.2. When this D / R is less than 0.2, there may be a problem that the seal member 30 is bent.

  An example of the seal member 30 having a quadrangular cross section perpendicular to the circumferential direction and having a notch in one ring-shaped portion mainly composed of carbon is called a gland packing. The gland packing is mainly divided into a “tape mold mold” and a “carbon molded product mold” depending on its manufacturing method. In the present invention, any one of these manufacturing methods may be adopted, or other manufacturing methods. May be adopted. The tape mold mold manufactures a gland packing by laminating tape-shaped carbon sheets in the circumferential direction and pressing and integrating them. On the other hand, a carbon molded product mold manufactures a gland packing by integrating carbon powder and / or carbon fiber by compression heating molding.

  Further, the size of the gland packing is preferably formed so that the inner circumference thereof matches the minimum value assumed as the outer diameter of the optical fiber preform 1 (that is, the minimum diameter of the optical fiber preform 1 to be used). . Depending on the size of the optical fiber preform 1, if the optical fiber preform has a diameter φ of about 140 mm, the outer diameter is 165 mm × the inner diameter is 135 mm × the height (thickness D) is 15 mm, and the width is R = 15 mm. The outer diameter is 170 mm, the inner diameter is 140 mm, the height (thickness D) is 15 mm, and the width is R = 15 mm. In any of these sizes, the above-mentioned ratio D / R is 1.

  In the example of FIG. 1, the width of the gap 15 is a value obtained by subtracting the diameter φ of the optical fiber preform 1 from the diameter d of the core tube 12 and halving it. For example, when the diameter φ of the optical fiber preform 1 is 140 mm and is formed with a diameter variation of ± 10 mm, the diameter d of the core tube 12 only needs to be about 160 mm, so the width of the gap 15, that is, (d− φ) / 2 is about 5 to 15 mm. The width R of the above gland packing needs to be equal to or larger than the width of the gap 15.

  Further, the inner diameter of the members inside the casing 27 other than the seal member 30 may be determined as appropriate so as to fill the gap 15. Since it is assumed that members other than the seal member 30 have no contraction force, the inner diameter of these members is the maximum value assumed as the radius of the optical fiber preform 1 (that is, the maximum of the optical fiber preform 1 used). (Diameter).

  As described above, in the present invention, even when the outer diameter φ of the optical fiber preform 1 changes, the seal member can always keep the contact with the optical fiber preform 1 as much as possible. That is, according to the present invention, even in the case of an optical fiber preform having a large diameter variation, the gap 15 generated between the upper end opening in the optical fiber drawing furnace and the optical fiber preform 1 can be sealed, It is possible to prevent outside air from getting into the furnace. This makes it possible to draw without deteriorating the carbon product in the furnace. Further, the seal member 30 is not only a simple structure as described above but also a structure that is not easily damaged. Thus, according to the seal structure 20 according to the present invention, the gap 15 can be sealed with the seal member 30 having a simple structure that is not easily damaged.

  Further, in the seal structure 20 according to the present invention, in order to ensure the flexibility of the seal member 30, a cut (cut portion 31) is provided in one place in the circumferential direction, but as illustrated in FIG. In order to prevent an airtight defect due to the cut portion 31, it is preferable that the cut portion 31 is covered with a sleeve 32 for use. That is, in the seal structure 20, it is preferable to provide the sleeve 32 so as to cover the cut portion 31 of the seal member 30. Examples of the material of the sleeve 32 include fibers such as alumina, carbon, ceramic, glass, and silica, textile materials, and nonwoven fabrics.

  In addition, although not shown, the seal member 30 may be provided with a plurality of rings stacked so as to shift the cut portion 31. That is, in order to ensure the flexibility of the seal member 30, a cut is provided at one place in the circumferential direction, but in order to prevent airtight defects due to the cut, a plurality of seal members 30 are prepared so that the cut portions do not overlap. You may devise, such as using it repeatedly. The configuration in which the sleeve 32 described above is provided and the configuration in which a plurality of seal members 30 are provided may be used in combination.

Actually, three seal members 30 with an inner diameter of 140 mm are used, and the cut portions 31 are arranged and laminated so that the angle formed by the cut portion 31 is 120 ° (divided into three equal parts of one round), and φ is 140 mm to 155 mm As a result of inserting and drawing the optical fiber preform 1 having the outer diameter variation, it was possible to perform good drawing without causing deterioration of the in-furnace carbon member due to airtight failure.
For comparison, three carbon sheets 63 with notches having an inner diameter of 140 mm shown in FIG. 4C are laminated, and an optical fiber preform 1 having an outer diameter variation in which φ is 140 mm to 155 mm is inserted. As a result of drawing, spikes during drawing frequently occurred from the beginning of drawing, and white smoke slightly rose from the upper part of the road and the drawing stopped. The carbon sheet 63 was partially bent, and it was confirmed that the carbon parts in the furnace were oxidized and consumed.

  Further, since the seal portion becomes hot, it is preferable that the seal member 30 and the sleeve 32 have a heat resistance of 200 ° C. or higher. In addition, when the thing which does not have high heat resistance is employ | adopted as the sealing member 30 or the sleeve 32, what is necessary is just to devise, such as providing the mechanism (for example, water cooling system) which cools them.

Next, the lid 40 of FIG. 1 will be described.
In the configuration in which the support rod 2 is provided on the optical fiber preform 1 as shown in FIG. 1, the support rod 2 is lowered to the position of the core tube 12 by the progress of the drawing process, that is, the support rod 2 is drawn. There is a scene located below the upper end portion 11a of the furnace body 10.

  In order to keep sealing the inside of the furnace even in such a situation, the optical fiber preform sealing structure according to the present invention preferably has a lid 40 in addition to the sealing structure 20 as shown in FIG. The lid 40 is a lid that penetrates the support rod 2 and is placed on the upper side of the optical fiber preform 1, and as shown in the figure, has a through hole 40a and a shoulder 40b for the support rod 2, The inner side is formed so as to fit into the sleeve portion 21. Examples of the material of the lid body 40 include quartz and metal.

By providing the lid 40, even if the drawing of the optical fiber 3 progresses and the optical fiber preform 1 and the support rod 2 are lowered, the lid is removed before the optical fiber preform 1 is detached from the seal member 30. 40 is fitted to the sleeve portion 21 and the lower end surface of the lid body 40 shifts to a state where it contacts the seal structure 20, so that the sealed state can be maintained.
In addition, although it demonstrated on the assumption that the cover body 40 has the shoulder part 40b, the cover body 40 may be a shape which just opened the through-hole 40a of the support bar 2 in the disk. Even in such a shape, transition between states as described above is possible as well.

DESCRIPTION OF SYMBOLS 1 ... Optical fiber preform, 2 ... Support rod, 3 ... Optical fiber, 10 ... Drawing furnace body, 11 ... Furnace housing | casing, 11a ... Upper end part, 12 ... Core tube, 13 ... Heater, 14 ... Thermal insulation, 15 DESCRIPTION OF SYMBOLS 16 ... Discharge hole, 20 ... Seal structure, 21 ... Sleeve part, 26 ... Carbon sheet, 24 ... Carbon sheet with a notch, 25 ... Quartz ring, 27 ... Case, 27a ... Gas inlet, 30 ... Seal member , 31 ... cutting part, 32 ... sleeve, 40 ... lid, 40a ... through hole, 40b ... shoulder.

Claims (7)

An optical fiber drawing furnace sealing structure for sealing a gap between an upper end opening of an optical fiber drawing furnace and an optical fiber preform inserted from the upper end opening;
A seal member mainly composed of carbon, which is a discontinuous ring obtained by cutting a part of the ring, is inserted in the radial direction of the seal member in a state where the optical fiber preform is passed through the inner peripheral side of the seal member. A sealing structure for an optical fiber drawing furnace, wherein an inner surface of the sealing member is in contact with a side surface of the optical fiber preform by contraction force.   2. The seal structure for an optical fiber drawing furnace according to claim 1, wherein a sleeve is provided so as to cover a cut portion of the seal member.   The seal structure for an optical fiber drawing furnace according to claim 1, wherein the seal member includes a plurality of cut rings, and is overlapped so as to shift a cut portion of the ring. .   The sealing structure of an optical fiber drawing furnace according to any one of claims 1 to 3, wherein the sealing member has a quadrangular cross section.   The seal structure for an optical fiber drawing furnace according to claim 4, wherein the ratio of the thickness of the cross section of the seal member to the width in the radial direction satisfies thickness / width ≧ 0.2.   The sealing structure for an optical fiber drawing furnace according to any one of claims 1 to 5, wherein the seal member has a heat resistance of 200 ° C or higher.   The optical fiber drawing according to any one of claims 1 to 6, wherein a ring-shaped member having heat resistance and not being discontinuous is further provided on an upper portion and / or a lower portion of the seal member. Furnace seal structure.

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